1. Field of the Invention
The present invention relates to using a supercritical fluid, typically water, with or without additives such as inorganic salts such as NaOH or KOH which increase the pH and the subsequent solvent capacity, selected hydrocarbons, or other soluble elements or compounds such as oxygen, air, carbon monoxide or carbon dioxide, to refine hydrocarbons such as heavy oil, bitumen and bitumen-like hydrocarbons.
2. Description of the Prior Art
World oil supply is changing, and the readily available medium to light crude oil reserves are getting harder to find and develop. Because the world energy demand is increasing, particularly in emerging economies such as India and China, exploitation of heavier oil reserves will be necessary to meet the demand as an alternative to more exploration and developing conventional oil reserves. Recovery and field development techniques for unconventional reserves have been progressing, such as with steam assisted gravity drainage (SAGD). Current refining technology, however, often is based on combinations of feed de-salting and high-vacuum distillation, followed by conventional hydrocracking, or a combination of coking and thermal cracking followed by some form of hydro-processing using various catalysts and process gases. Known techniques require complex, expensive equipment and an involved refinery infrastructure that includes capacity to produce hydrogen, heating fuel and maintain equipment and supplies. Conventional approaches also generate large amounts of carbon dioxide from the heating required to drive the main distillation column, as well as associated upstream and downstream processing.
Against the foregoing background, the methods and apparatuses disclosed hereinafter were developed. The disclosed methods and apparatuses produce similarly desirable products with fewer processing steps and therefore lower costs, increase worker safety due to fewer process steps and less reagent handling, allow greater opportunity for new oil field development and subsequent positive economic impact, and reduce the amount of carbon dioxide and associated waste products typically associated with conventional refineries.
U.S. Pat. No. 3,989,618 discloses a process for upgrading a hydrocarbon fraction by contacting the hydrocarbons with supercritical water over a temperature range of 600° F. to 900° F. with no catalyst of added hydrogen. However, other additives are an important part of the process; the patent discloses that it is useful to add a biphenyl, pyridine, partly hydrogenated aromatic oil, or a mono- or polyhydric compound such as methanol to the water to aid in the hydrocarbon upgrading process. This method requires the use of carcinogens such as aromatic hydrocarbons to aid the reaction process. The aromatic hydrocarbons provide an in-situ source of hydrogen, with a penalty of having to add reagents to allow operation at lower temperatures and pressures. In addition, the process does not provide a method for handling the unreacted portion of the feed, or a means to control the reaction so that the product distribution can be controlled.
U.S. Pat. No. 4,818,370 discloses a process for upgrading heavy oil in a subterranean reservoir using supercritical “brine” in combination with in-situ combustion to provide heat. The brine is salt water typically found in oil reservoirs. An oxidizing gas is injected into the underground oil reservoir to enable a combustion zone that heats the heavy oil to allow it to drain into the combustion zone (which already contains the brine), and the brine and oil are heated and pressurized to supercritical conditions. After a suitable time, the heavy oil is converted to lighter components that are removed from the reservoir using conventional recovery methods. This method is limited to working with heavy hydrocarbons in-situ, and the efficiency of the method is dependent on the reservoir conditions and physical properties. No method is described to provide control of the reaction conditions such as the rate, contact times, reagent ratios, temperature, or pressure. It would be difficult to ensure that optimal conditions are maintained to get the best product distribution. In addition, the process requires additional means to inject oxidizing gases and recover the combustion gases that contribute to the carbon footprint of the process.
U.S. Patent Application Publication 2007/0056881 A1 discloses a method for upgrading heavy hydrocarbons and the like using a flow-through reactor to contact heavy hydrocarbons with water at temperatures ranging from 250° C. to 450° C., and pressures ranging from 500 psi to 3000 psi. The method uses a simple reactor with inlet ports for the water and the hydrocarbons into the reactor, and an outlet port that directs the water-oil mix to a cooler that cools the mixture and allows separation. Other conditions described are residence times from 28 seconds to 10 minutes, and the additional allowance to introduce carbon monoxide or selected inert gases such as nitrogen into the reactor. However, the publication does not describe means to control the product distribution or quality, nor means to deal with unreacted heavy hydrocarbons. It is known that any heavy oil or bitumen processing method produces coke or other refractory carbonaceous material that must be handled in some fashion. This publication does not describe a method for handling carbonaceous residues that can be deleterious to reactor operation.
U.S. Pat. No. 7,754,067 discloses a system and method for upgrading heavy hydrocarbons and the like using supercritical water, with means for contacting the hydrocarbons and supercritical water in two separate heating stages. In a first zone, heavy hydrocarbons are mixed with supercritical water at pressures above 22.1 MPa at temperatures up to 775 K, and then in the second zone, the mixture is heated either by an external source or by bleeding in oxygen to heat the fluid in situ up to 870 K to 1075 K. The system also has a convoluted or multi-pass contacting device with a nozzle to try to disperse the hydrocarbons into the supercritical water. The method is limited by the formation of solid carbonaceous materials that necessitate the shutdown and clean out of the reactor. The multi-pass portion required to effect the necessary mixing also limits the means to effectively clean and maintain the contacting device. In addition, the heating profile described is complex and requires shortened heat-up times between the heating stages to reduce coke formation. This limits the operating time and potential throughput of the method.
U.S. Pat. No. 7,144,148 discloses a method for upgrading heavy oil and the like using a supercritical solvating hydrocarbon, and means for contacting the heavy oil and solvating solvent using a fluidized bed of hot solids. The heavy hydrocarbons are contacted with the supercritical solvating hydrocarbon in a first fluidized bed at temperatures at or below 538° C., with the solid particulates providing a method for heat transfer. After reaction, the lighter hydrocarbons are removed and the solids transported to a second bed to remove accumulated coke formation. This method, however, is limited by using a solvating hydrocarbon to essentially dissolve and then react with the heavy hydrocarbons. This necessitates a solvent removal and recycle step along with handling the solid particulates used to transfer heat to the reaction mixture. An additional solids removal step is required to prevent the solid particulates from affecting downstream processing.